Telephone system



April 18, 1939. R, TAYLOR 2,154,786

TELEPHONE SYSTEM Filed Dec. 11, 1936 2 Sheets-Sheet l lc rem- 4 T A V 000-1 I I v w B L v T c 1c uwp f/vv/v'ro/?- Patented Apr. 18, 1939 UNITEDSTATES PATENT OFFICE TELEPHONE SYSTEM Application December 11, 1936,Serial No. 115,323 In Great Britain January 11, 1936 8 Claims.

The present invention relates to telephone systerns and is moreparticularly concerned with two-party line systems in which separatemeters are provided for the two parties and no special operations arerequired of the subscriber for either incoming or outgoing calls. Thechief object of the invention is to provide for correct operation in thecase of re-ringing over a party line from a trunk operators position.

According to one feature of the invention in a telephone systemincluding two-party lines arranged for individual signalling of theparties, a relay group in the outgoing circuit responsive to ringingcurrent permits the two subscribers to be signalled individually overthepath over which an outgoing call has been set up.

According to another feature of the invention in a telephone systemincluding two-party lines arranged for individual signalling of theparties, a relay group is provided whereby if a connection has been setup to an operator a re-ringing operation performed by the operator afterthe calling party has replaced his receiver effects the signalling ofthe original calling party only.

The invention will be better understood from the following descriptionof one method of carrying it into effect, reference being had to theaccompanying drawings comprising Figs. 1 and 2. Fig. 1 shows the circuitconnections of the telephone instruments of the two party-linesubscribers X and Y who share a single pair of conductors extending tothe main exchange, while Fig. 2 shows the equipment at the main exchangewhich is interposed between the party line and the exchange line relayequipment.

Referring to Fig. 1, it will be appreciated that the instruments of thetwo subscribers are identical except for one slight wiring differenceand that they are connected diflferently to the exchange line. Thusunder normal conditions the bell B of the X subscriber is connected fromearth to the B leg while that of the Y subscriber is connected to the Aleg. When the X subscriber removes his receiver to originate a call, the5 switchhook springs SH are operated and a loop is extended over the Aand B legs to the main exchange whilst during dialling earth pulses aretransmitted over the B leg. Upon removal of the Y subscribers receiver,a loop is extended to the main exchange whilst during dialling loopimpulses are transmitted. It will be seen that the instrument circuitsof the two parties are substantially identical, discrimination betweenthem being effected as regards incoming calls by a reversal of the A andB leads and as regards outgoing calls by a change of strapping on theterminal block provided.

It will be understood that relay P in Fig. 2 may be connected either tothe P lead as indicated by the chain-dotted line or to the meter lead Mas =5 indicated by the circle and dot line. The former connection willallow the party line set to work into an existing exchange in which uponthe operation of the line relay earth is applied to the P contact in thefinal selector multiple to busy the 10' line. If however as will beassumed in the following description the main exchange employs linefinders arranged to busy the final selector P contact by disconnectionof the cut-off relay battery as soon as the line relay operates and toconnect II earth to the M lead immediately the calling line is found,the later connection is employed.

It will first be assumed that the X subscriber initiates a call byremoving his receiver from the switchhook whereupon a loop is completeover Q the line as follows:--Earth in the line relay set (not shown),positive lead, armature x12, lower winding of relay X, armature acyZ, Bleg of the line, impulse springs IS, transmitter T, switchhook springsSH, induction coil IC, A leg, arma- Q5 ture .rzjl, windings of relays Aand X, armature 1T3, negative lead to battery by way of the mainexchange line relay which is also not shown. Relay A and the line relayoperate in this circuit but not relay X which is differentially wound.Armature at operates relay B which connects relay P to the meter lead Mwhile the energisation of the line relay initiates the operation of theline finder to hunt for the calling line. When it is found the Xsubscriber is connected through 85 to a first selector and receives dialtone and at the same time earth is returned over the M lead to operaterelay P which at armature p5 prepares a circuit for relay XY.

The subscriber now dials the first digit of the it) wanted number and assoon as his dial is moved off-normal, direct earth is applied by way ofthe shunt springs SS to the B leg, and over transmitter T to the A leg.Relay A and the selector line relay are maintained operated but relay Xis now 15 unbalanced and at armature .rl operates relay XR. Relay XRcompletes a circuit for relay XY at armature x1! and at armature m2disconnects the positive lead to the first selector and applies a localearth to hold the selector line relay over 50 its battery-connectedwinding when the subscribers dial returns to normal and replaces theearth conditions by a loop. A further function of armature M2 is toprevent the earth which is applied to the A leg during dialling fromshunting the ii earthed winding of the selector line relay and causingthis relay to be so sluggish as to fail to respond to the impulsestransmitted by the subscriber. On the operation of relay XY the leadsextending to the first selector are reversed at armatures xyl and $112while armature x144 extends the M lead through to the X subscribersmeter. While the dial is returning to normal, earth pulses aretransmitted over the B leg and armatures :tyZ and p3 to impulse theselector line relay over one winding. Subsequent digits dialled resultin further automatic switches being set up to establish connection withthe called subscriber who will then be rung in the usual manner. Uponhis reply a metering potential will be applied to the M lead to energisethe X meter over armature r114. Relays A and X in the party line relayset may chatter during dialling but relay B will hold operated duringeach pulse train due to its slug and relays P and XY are already lockedup. On the completion of dialling each train when the loop conditionsare restored,-relay X will release and in turn release relay XR.

Should the X subscriber desire to make a trunk call, the digits requiredto route the call 'to a manual board are dialled. Assuming now that thecall cannot be completed on demand the operator tells the subscriber tohang up and relays A and B in the party line set release. The operatorhowever maintains the earth on the M lead and relays P and KYaccordingly remain operated while armature bl connects the re-ring relayRR to the outgoing negative lead by Way of condenser QB. Hence when theoperator operates her ringing key to re-call the X subscriber therebyconnecting the earthed ringing generator to the negative lead, relay RRwill operate, its operation being rendered steady by the rectifier MRCwhich is connected in parallel. Armatures M2 and W3 short-circuitcondenser QA and relays A and X and the ringing current is thustransmitted over armatures p3 and $112 to the B leg to actuate the bellof the X subscriber only. Armature 113 also removes the short-circuitfrom the ring-trip relay F which is thus included in series with theline but does not operate on alternating current only. When the Xsubscriber answers, the high impedance bell B and condenser C will bereplaced by a direct current loop and relay F immediately operates overits upper winding in series with the ringing return battery. Thereuponat armature fl it renders its lower winding effective and at armature f2opens the ringing circuit to the X subscriber. This relay servestoprevent the ringing current passing through the X subscriberstransmitter to the A leg and ringing the Y subscribers bell. Relay RRremains operated and maintains relay F energised until the operatorrestores her ringing key whereupon relays RR and F release. Armature rr3now transfers the short-circuit from relay A to relay F and relay Are-operates over the X subscribers loop in series with the battery feedrelay and also relay X which does not now operate. The energisation ofrelay A operates relay B which at armature b'l opens the circuit ofrelay RR. The operator completes the trunk connection and conversationmay now proceed.

Considering now the case of a call by the Y subscriber, when he removeshis receiver a loop is completed to: operate relay A and the line relayas before. Relay A operates relay B and when the line finder finds thecalling line, relay P is operated and dial. tone is returned to thesubscriber exactly as in the case of a call by the X subscriber.

The Y subscriber now dials, and loop impulses are transmitted over the Aand B wires to actuate the selector impulse relays. Relay X howeverremains unresponsive and hence relays XR and XY do not operate and themeter lead is connected over the back contact of armature $114 to the Ysubscribers meter and thus when the called subscriber answers this meterwill be energised.

Under operator re-ring conditions since relay XY is unoperated, theringing current will be extended over the A leg to ring the Ysubscribers bell only, and when he removes his receiver, relay F willtrip the ringing as previously described and will be released when theoperator restores her ringing key.

It will be appreciated that if while one party is awaiting recall by theoperator the other party removes his receiver to initiate a call, thislatte-r party will understand from the absence of dial tone that theline is not available for his use. This condition is not greatlydifferent from that which arises if one party attempts to initiate acall while the line is in use by the other party and is not likely tocause difliculty in practice.

At the completion of conversation when the calling Y subscribe-r hangsup the calling loop is disconnected and relay A and the battery feedrelay releases. After a short period relay B releases and also earth isremoved from the M lead to release relay P whereupon the circuit isready to deal with another call. When the X subscriber hangs up at theend of a connection, in addition to the relays mentioned above relay XYhas also torelease before the party line set is restored to normal. Thearmatures xyl and $1112 and p3 and p4 which together constitute a meansof reversing the A and B legs serve to prevent a loop being momentarilyextended forward again and complicating the release of the switch when acalling X subscriber concludes conversation and restores his receive-ras would occur if armatures. of relay XY only were used.

Considering now incoming calls to the party line subscribers, it will benoticed that the positive and negative leads extending from the finalselector multiple are reversed as regards the two sets of contactsallotted to the subscribers in this multiple. Ringing current is appliedfrom the final selector over the negative lead and it will therefore beseen that when the X subscribers number is dialled ringing current willbe connected to the B leg and when the Y subscribers number is dialledringing current will be connected to the A leg.

The rectifiers MIRA and MRB serve to prevent the re-operation of relay Xshould an X subscriber accidentally actuate his dial after a connectionhas been completed. When the called subscriber answers, the battery feedfrom the final switch in the train is reversed as is well known, andwill therefore connect the earthed winding of the battery feed relay tothe negative lead and the battery-connected winding of this relay to thepositive lead. Should the calling dial be moved off normal for anyreason, earth will be extended over the A and. B wires and overarmatures :vyl and p4, lower winding of relay X, positive'lead, to thebattery-connected winding of the feed relay. Any tendency for relay X tooperate is prevented by rectifier MRB which is now in a conductivedirection and effectively short-circuits thelower winding of relay 1 Xwhile the upper winding of relay X is shortcircuited by the rectifierMRA. It is important that relay X should not operate since the resultantoperation of relay XR would open the holding circuit for the batteryfeed relay in the final switch at armature m2 and the connection wouldbe broken down.

In order to minimise transmission loss by transformer action of thewinding of X during speech, nickel iron sleeves are fitted on relay A toincrease its impedance.

I claim:

1. In a telephone system, a two-party line, an outgoing circuit for saidline for setting up outgoing calls from both parties on said line, arelay group in said outgoing circuit operated in accordance with theparty making an outgoing call, and means in said relay group responsiveto signalling current connected to said outgoing circuit for signallingeither party dependent upon the operated condition of said relay group.

2. In a telephone system, a two-party line, an outgoing circuit for saidline for setting up outgoing calls from both parties on said line, arelay group in said outgoing circuit operated in accordance with theparty making an outgoing call, an operators poistion connected with inresponse to said outgoing call, and means in said relay group responsiveto a re-ringing operation performed by the operator after the callingparty has replaced his receiver for signalling only the original callingparty.

3. In a telephone system as claimed in claim 1 wherein said party linecomprises only two conductors and said signalling current is connectedto either one of said conductors dependent upon the operated conditionof said relay group.

4. In a telephone system wherein battery feed is reversed to the callingline on the reply of the called party in an established telephoneconnection, a calling line, a discriminating relay having two windingsassociated with said line, a circuit for operating said relay, a dial onsaid line efiective to complete said circuit and energize said relayduring the establishment of a connection to a called line, and arectifier connected in shunt of each winding to prevent energization ofsaid relay in case said dial is operated after the battery feed in anestablished connection has been reversed on the reply of the calledparty.

5. In a telephone system as claimed in claim 1 including adiscriminating relay in said relay group, means for operating said relayonly in case a certain one party on said line makes an outgoing call,and means controlled by the operation of said relay for reversing theconnections to the line conductors of said party line.

6. A telephone system as claimed in claim 2 including a ring-cut-offrelay in said relay group operated in said re-ring operations inresponse to the calling party replying, and means controlled by saidring-cut-ofi relay for cutting off said ringing current to preventsignalling the other party on said party line.

'7. In a telephone system, an exchange, a party line comprising twoconductors terminating in said exchange, a first and a second substationon said line, a dial at each substation, a set of outgoing terminals forsaid line over which outgoing calls are extended, a relaygroup'individual to said line connecting said line conductors to saidoutgoing terminals, a discriminating relay in said relay group onlyoperated in case the dial at a particular one of said substations isoperated during an outgoing call, and means in said relay groupcontrolled by the operation of said relay for reversing the connectionof said line conductors to said outgoing terminals.

8. In a telephone system, an exchange, a party line comprising twoconductors terminating in said exchange, a first and a second substationon said line, a signalling circuit for the first substation includingthe first line conductor and a signalling circuit for the secondsubstation including the second line conductor, means for operating theringers at each substation over their respective signalling circuits onincoming calls, and a relay group individual to said line operated inaccordance with the particular substation making an outgoing call toprepare a ringing circuit to signal said particular substation over itssignalling circuit in case ringing current is connected to said relaygroup after said calling substation receiver is replaced.

REGINALD TAYLOR.

